JP2874206B2 - Oxygen concentration sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen concentration sensor, and more particularly, to an oxygen concentration sensor configured to protect an electrode with a protective member.

[Conventional technology]

2. Description of the Related Art As an oxygen concentration sensor for detecting an oxygen concentration in exhaust gas of an internal combustion engine, a sensor using an oxygen ion conductive solid electrolyte (for example, zirconia: ZrO ₂ ) is known. This oxygen concentration sensor has a structure in which electrodes are disposed on both surfaces of the solid electrolyte, and an exhaust gas is introduced into one electrode and a reference gas (atmosphere) is introduced into the other electrode. It is configured. The solid electrolyte is configured to detect the oxygen concentration in the exhaust gas by utilizing the property of generating an electromotive force due to the difference in oxygen concentration between the two surfaces.

Further, since the oxygen concentration sensor is provided in an exhaust pipe having severe environmental conditions, a protection member is provided on the side to which the exhaust gas of the solid electrolyte is introduced to protect the electrode.

As a method for forming the protective member on the solid electrolyte, for example, as shown in JP-A-56-96240, a porous layer (allowing the passage of gas) is adhered to the entire surface of the solid electrolyte as a protective member. A forming method of performing integral firing is known. However, in the oxygen concentration sensor 1 disclosed in the publication, when this is mounted on the exhaust pipe 2, the porous layers 3 and 4 penetrate from the exhaust gas side to the atmosphere side as shown in FIG. The atmosphere enters the exhaust gas side through the porous layers 3 and 4 (the state of the entry of the atmosphere is indicated by arrows), adversely affects the sensor characteristics and lowers the reliability.

Therefore, as shown in FIG. 9, on the exhaust gas side of the solid electrolyte 8, the porous layer 6 (shown in satin) is provided only in the portion that actually contributes to oxygen concentration detection (the portion where the electrode 5 is provided). And
An oxygen concentration sensor 9 (only the electrode cell portion in FIG. 9) is configured so that the dense layer 7 (which blocks the passage of gas) is separately provided in other portions so that the atmosphere does not enter the exhaust gas side. Illustrated) has been developed.

[Problems to be solved by the invention]

However, in the conventional oxygen concentration sensor 9 shown in FIG. 9, since the two types of layers 6 and 7 having different properties are separately formed on the solid electrolyte 8, the two layers 6 and 7 contract after firing. There was a problem that a gap was generated at the boundary between the two due to the difference in the rates. When a gap is generated, the exhaust gas directly contacts the electrode 5 through the gap, so that the electrode 5 is easily deteriorated, and the layers 6 and 7 do not function effectively as protective members. Also, if another ceramic layer is laminated on the boundary portion simply to fill the gap, or if the layers 6 and 7 are partially overlapped and fired, the gap caused by the difference in shrinkage still remains. Will occur.

The present invention has been made in view of the above points, and an object of the present invention is to provide an oxygen concentration sensor that can effectively protect an electrode formed on a solid electrolyte.

[Means for solving the problem]

In order to solve the above problems, in the present invention, first and second electrodes are provided on both surfaces of an oxygen ion conducting solid electrolyte, and a protection member for protecting the first electrode is provided.
An oxygen concentration sensor for introducing an exhaust gas to the electrode side through the protective member and introducing a reference gas to the second electrode side to detect the oxygen concentration in the exhaust gas; A gas introduction portion is a porous layer, and a portion other than the introduction portion is a dense layer, and the porous layer and the dense layer are continuously integrated at a boundary portion thereof. Is what you do.

[Action]

In the oxygen concentration sensor having the above configuration, the protection member is
It is composed of a porous layer that allows the passage of exhaust gas and a dense layer that blocks the passage of exhaust gas. The porous layer and the dense layer are not separately formed but are continuously integrated.
Therefore, no gap is formed between the porous layer and the dense layer, and the exhaust gas is not directly introduced into the electrode, so that the electrode can be protected reliably. When the oxygen concentration sensor is mounted on the exhaust pipe, the dense layer is located at the boundary between the atmosphere side and the exhaust gas side, whereby the intrusion of the atmosphere into the exhaust gas side can be prevented.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings. Longitudinal sectional view of FIG. 1 is an oxygen concentration sensor 10 which is an embodiment of the present invention (hereinafter, referred to as O ₂ sensor), Figure 2 is O ₂ sensor 10
FIG. 3 is an exploded perspective view of the O ₂ sensor 10.

The O ₂ sensor 10 includes a flat bottom plate 11, an air inlet 12 having a U-shaped plane, a first electrode 13 made of platinum, a second electrode 14 also made of platinum, a flat reaction plate 15, It is composed of a protection plate 16 and the like which are features of the present invention. In addition, the first and second
The electrodes 13 and 14 and the reaction plate 15 constitute a detection cell unit 17.

Of the above-mentioned components, the bottom plate 11, the air introduction unit 12, the reaction plate 15
Is a green sheet of zirconia (ZrO ₂ ), which is an oxygen ion conductive solid electrolyte (100 parts of ZrO ₂ powder, binder 11
Parts, solvent 70 parts, plasticizer 15 parts, peptizer 3 parts by ball mill
(Formed with slurry stirred for 50 hours). The first and second electrodes 13 and 14 are respectively formed at predetermined positions on both sides of the reaction plate 15 by a screen printing method.

The protective plate 16 which is a feature of the present invention includes a porous layer 18 (in the figure,
And a dense layer 19, and the layers 18, 19 are formed so as to be continuously integrated by a manufacturing method described later, and constitute one continuous plate-shaped material. Porous layer 18
Is porous (average pore size 3000
Å or more). Further, the disposition position is selected at a position where the exhaust gas is introduced, specifically, at a position on the left side in FIG. 3 facing the wide portion 13a of the first electrode 13. A region other than the porous layer 18 of the protective plate 16 is constituted by a dense layer 19. Almost no pores are formed in the dense layer 19, so that the exhaust gas
Can not pass through.

Next, a method of manufacturing the protective plate 16 having the above configuration will be described with reference to FIG. Since the firing method and the like are not different from known methods, the manufacturing method described here describes a method of manufacturing the protective plate ceramic green sheet 20 (hereinafter simply referred to as a sheet), which is the protective plate 16 before firing. I do.

To manufacture the sheet 20, first, a slurry 21 for a dense sheet and a slurry 22 for a porous sheet (shown as satin in the figure) are manufactured as slurries for sheet manufacture. Each slurry 2
1,22 are both 100 parts ceramic powder (zirconia powder),
It consists of 11 parts of binder, 70 parts of solvent, 5 parts of plasticizer and 3 parts of deflocculant, but the stirring time in the ball mill is different. That is, the dense sheet slurry 21 is stirred for 50 hours, and is sufficiently stirred so as not to generate pores inside. On the other hand, in the porous sheet slurry 22, the stirring is
This is performed only for 40 minutes, so that the porous sheet slurry 22 is configured such that pores are generated inside the slurry 22 after firing.

The dense sheet slurry 21 serves as a base material of the bottom plate 11, the air introduction section 12, and the reaction plate 15, and the ceramic green sheets of the respective components described above are also known from the dense sheet slurry 21. It is formed by a manufacturing method.

When the slurries 21 and 22 are manufactured as described above, the slurries 21 and 22 are placed in the slurry receiver 23 of the doctor blade device.
Is loaded. At this time, a partition plate 24 (about 1 mm thick) is provided in the slurry receiver 23 so that the slurries 21 and 22 do not mix. The slit of the blade 25 is set to 0.9 mm. Then, the casting film 26 is fed in the direction of arrow A in the drawing at a speed of 0.3 mm / min and dried at about 120 ° C. with hot air to produce a sheet 20 having a thickness of 300 μm.

In the manufacturing process of the sheet 20, when each of the slurries 21 and 22 is disposed at a predetermined thickness on the casting film 26 by the blade 25, each of the slurries 21 and 22 is
(In the vicinity of the position indicated by the broken line in the figure). Therefore, the sheet 20 is a slurry 21 for the dense sheet.
And the slurry 22 for the porous sheet is continuously integrated. Accordingly, the boundary layer 27 has a configuration in which the content of the internal pores (porosity) continuously decreases from the porous slurry 22 to the dense sheet slurry 21. Therefore, by baking the sheet 20 having this structure, the continuous protective plate 16 can be obtained by integrating the porous layer 18 having many pores and the dense layer 19 having no pores.

As described above, in order to manufacture the protective plate 16 in which the porous layer 18 and the dense layer 19 are integrated, two types of slurries 21 and 22 are simply produced, and the two types of slurries 21 and 22 are formed. It can be easily manufactured without changing the conventional manufacturing process greatly, only by loading it into the 23.

In addition, viscosity generally becomes a problem as a characteristic of the slurry, and it is necessary to select this viscosity to an appropriate value especially in the sheet 20 in which two types of slurries 21 and 22 are partially mixed. 5 and 6 show the relationship between the smoothness of the green sheet, the width of the boundary layer 27 and the viscosity of the slurry. Here, the viscosity of the slurry is a value indicating the fluidity of the slurry. In other words, the lower the viscosity is, the smoother the slurry is and the higher the fluidity is. The higher the viscosity is, the rougher the slurry is and the lower the fluidity is. As a characteristic of the ceramic green sheet, it is desirable that the smoothness is good in order to improve the adhesion between the layers when the sheets are laminated, and that each slurry is
It is desirable that the width of the boundary layers 27 of the layers 21 and 22 is small. Therefore, referring to FIG. 6, in order to reduce the width of the boundary layer 27 while maintaining the smoothness of the green sheet, it is necessary that the viscosity of each of the slurries 21 and 22 be set between about 2000 cps to 3000 cps. I understand.

The components manufactured as described above are arranged in the order shown in FIG. 3, and 5k using a cellulose-based adhesive.
After pressure bonding for 30 minutes at a pressure of g / cm ² , degreasing is performed at a temperature of 20 ° C./hour and a maximum temperature of 420 ° C., followed by firing at 1400 ° C. for 1 hour. Thereby, each component is sintered and integrated,
The O ₂ sensor 10 shown in FIGS. 1 and 2 is formed.

FIG. 7 shows a state where the O ₂ sensor 10 is mounted on the exhaust pipe 28. The protective plate 15 provided on the O ₂ sensor 10 has a porous layer 18.
And the dense layer 19 are integrated, so that both layers 1
There is no gap at the boundary between 8,19 and the exhaust gas is directly
Is not introduced to the electrode 13 of the first electrode. Accordingly, the first electrode 13 by a protective plate 16 is securely protected, it is possible to improve the durability of the electrodes 13, also improves the reliability of the O ₂ sensor 10.

Further, focusing on a boundary portion between the atmosphere and the exhaust gas, the dense layer 19 is configured to be located at a portion penetrating from the atmosphere side to the exhaust gas side. As described above, since the dense layer 19 blocks the passage of the exhaust gas, the atmosphere does not enter the exhaust gas side via the O ₂ sensor 10 at this boundary portion, and the detection accuracy and the response of the sensor are reduced. And stable sensor characteristics can be obtained.

〔The invention's effect〕

As described above, according to the present invention, since the boundary between the porous layer and the dense layer has a continuous and integral structure, the first electrode on the exhaust gas side does not directly contact the exhaust gas,
It has the features that the durability of the electrode can be improved, and that when the O ₂ sensor is mounted on the exhaust pipe, the air does not enter the exhaust gas side and stable sensor characteristics can be obtained.

[Brief description of the drawings]

1 is a longitudinal sectional view of an O ₂ sensor according to an embodiment of the present invention, FIG. 2 is an external view of the O ₂ sensor shown in FIG. 1, and FIG.
FIG. 4 is an exploded perspective view of the O ₂ sensor shown in FIG. 4, FIG. 4 is a view for explaining a method of manufacturing the protective plate, and FIG. 5 and FIG. FIG. 7 is a diagram showing a state in which an O ₂ sensor is mounted on an exhaust pipe, and FIGS. 8 and 9 are diagrams for explaining an example of a conventional O ₂ sensor. 10: oxygen concentration sensor (O ₂ sensor), 11: bottom plate, 12: atmosphere introduction part, 13: first electrode, 14: second electrode, 15: reaction plate, 16: protection plate, 18: porous layer , 19: dense layer, 20: ceramic green sheet (sheet) for protective plate, 21: slurry for dense sheet, 22: slurry for porous sheet, 23: slurry receiver, 24: partition plate, 27: boundary layer.

Claims (1)

(57) [Claims] An oxygen ion conducting solid electrolyte is provided with first and second electrodes on both surfaces thereof, and a protective member for protecting the first electrode is provided. An oxygen concentration sensor configured to detect the oxygen concentration in the exhaust gas by introducing a reference gas to the second electrode side, wherein an exhaust gas introduction portion of the protection member is formed of a porous layer. And a portion other than the introduction portion is a dense layer, and the porous layer and the dense layer are continuously integrated at a boundary portion thereof.